1. Field of the Invention
The present invention relates to clock signal derivation systems used in the receiving section of a data transmission system, and more particularly to a clock signal derivation system for deriving a clock signal from a Manchester coded signal or the like having a clock frequency of twice the bit rate.
2. Description of the Prior Art
For deriving clock information from an input signal of base band in a digital transmission, there have been proposed two types of systems; use of a full-wave rectified signal (analog operation) and use of transition points on waveform (differentiated waveform) (digital operation). However, these methods have a drawback. When a Manchester coded signal of twice the information rate, binary AMI (Alternate Mark Inversion) coded signal or split phase coded signal is used for a base band signal, there is a possiblity in the above two methods, that phase inverted clock information is detected as correct clock information. This is caused by the fact that in a method using a full-wave rectified signal, positive and negative waves are asymmetrically rectified and in the method of using transition points in the waveform, unwanted waves are passed due to the characteristics of the the succeeding stage of clock wave filter and amplifier.